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Stefan-Boltzmann Law Part I


This came up in the climate-change discussion group I've mentioned before.

One participant in a heated exchange, seeking to boost his own scientific cred, challenged the other to explain the Stefan-Boltzmann Law. The second fellow refused to participate in that discussion, saying, "I suspect you copied the question from elsewhere, and would be unable to actually converse on the topic ... are you real or are you Memorex?"

That last reference tells me something about his age, at least.

Anyway, now I'm curious, so I do a little research. The S-B Law describes the radiation from a black body as directly proportional to the fourth power of that black body's thermodynamic temperature. Huh?

A "black body" is an ideal state, somewhat akin to those "frictionless surfaces" you encounter in "Intro to Physics" courses. But you don't get to this ideal state until you get to "Intro to Thermodynamics."

A black body is one that absorbs all incident radiation. A white body, on the other hand, reflects all incident rays. Most actual bodies are thermodynamically gray. For many gray bodies the S-B law works as a good approximation.

So, the law basically says that radiation does the job if reflection fails. That is: if a body doesn't reflect energy away, then it becomes hotter over time, and as it becomes hotter, it radiates energy outward, creating the constant mathematical relationship with which we began.

Curiosity sated? Well ... just a bit.

But what does all this have to do with global warming? Or was it just an arbitrary quiz that one internet blowhard was trying to administer to another?


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